There is a continuing demand for accurate route data for use in the production of digital maps. Portable navigation devices (PND), such as dedicated portable satellite navigation devices, in-built vehicle navigation systems and smartphones incorporating global positioning system (GPS) receivers and mapping software have become commonplace. These devices provide navigational instructions using digital maps that may be stored remotely and accessed via a wireless network, or stored locally on the device. These maps typically have relatively reliable information concerning the existence and locations of various routes in a navigable network; such as roads, highways or paths. Route information is currently typically stored in digital map databases as a sequence of nodes pinpointing the centreline of a route (typically detected using GPS probe data), views of which are generated by joining the nodes using, for example, a spline function, which is then usable to render a simple view of the route as a line along which the PND progresses in transit. However these map resources and views often lack more detailed information such as the number of lanes on the road or road sign content. Further, there is a desire to include additional information to these digital maps, so as to build up-to-date realistic views of routes. As the prevalence of these devices ever increases and road layouts continue to change, there is a persistent need for more data to update the maps to the best available accuracy.
A potential source for route data used to generate detailed views of digital maps is satellite imagery of the Earth. This technique is relatively accurate in identifying the location of roads or ‘routes’ for building a digital map and in providing views of these routes. Satellite imagery, however, has various disadvantages to it. By their very nature, satellites can only offer a view of a route from above. Areas of the route that are obscured by the presence of intervening matter, such as tunnels, trees, bridges, clouds, etc, or features which are not be visible from above, such as road signs, or which require a higher resolution than is available will not be imaged. These images are also generally costly and time consuming to acquire in practice, so are rarely up to date.
Third parties, such as governments or local authorities, are a potential further source of route data. These parties may notify the map makers of the existence of new routes, or to the presence of road works or various other features on a map. Such data is typically unreliable however, often unavailable and does not generally offer views of routes.
Route data can also be collected from mobile mapping vehicles. These vehicles have been used in abundance by Google™ in the creation of their Street View™ images. Multiple images of a route are acquired across a 360 degree view using a moving van with several cameras mounted to it. Positional data is acquired from GPS data and fused to these images so as to build a realistic view of the route in the digital map. Although mobile mapping vehicles are able to offer roadside views of a route at higher level of detail than is available from satellite images, they share two other disadvantages with satellite images; namely their high cost and the time consuming method by which the images are obtained. This, in practice, means that the route data acquired also quickly falls out of date and is rarely updated.
There therefore is a need for an alternative means for obtaining route data for use in the production of detailed and up-to-date views of a digital map that overcomes the abovementioned limitations in the art.